safety wired bolts

[hprass]

Looking at an old DC 3 engine at the Teterboro Air Museun, I noticed the twisted wiring from bolt to bolt. Because of the configuration its purpose was quickly apparent. The internet provided much more info re a subject of which I had been completely unaware. It offered that aircraft and racing cars are so equipped because of vibration.
QUESTION:
Does this apply to regular in-line engines in small aircraft or just to radials? What about jets that presumably have less of the destructive vibration.
I assume that regular automotive engines are exempt because they are seldom run at close to full power.
HP

[lnuss]

Safety wiring is used extensively on most aircraft, whether a J-3, a DC-3 or a jet. Virtually everything mounted in a Boeing B-47, for instance, was safety wired, from mounting brackets to cannon plugs (electrical wiring) to you name it -- safety wire was an integral part of our tool pouch. A Super Cub (as well as other light aircraft) has safety wire on engine mounts, oil filter, propeller bolts and many, many other things. There are a few areas where locknuts are used instead, on some aircraft, and there are also areas where cotter pins are used with castle nuts (wheel hubs, for example) -- it's all up to the manufacturer and the FAA certification process.

As you mentioned, it's largely because of vibration, and the fact that you cannot pull off to the side of the road if something comes loose.

Full power on engines has little to do with it, partly because engines aren't the only things that cause vibration -- safety wire is used on gliders, too. Cars don't go through a certification process (at least not in the sense that an aircraft does), so "exempt" means little. And you can always pull off to the side of the road in a car. Still, you'll find locknuts in a lot of places on cars, and cotter pins, too.

[hprass]

Thanks Larry, great response!!!

HP

[FITZY]

"Virtually everything mounted in a Boeing B-47, for instance, was safety wired...."

Ditto for the T-33, F-105, C-130, and KC-135. There is even a specialized locking pliers that spins to make the tight twists. Some cockpit switches were wired OFF with special lightweight wire that could be broken in an emergency, but prevented indadvertent switching under normal operations.

[EMAPhil]

Many of todays applications use locking tab washers or locking wire thread inserts so pure wire is disappearing. Pity in some ways because it does often provide a visual clue that a nut is moving.

I'm a graduate Mechanical Engineer and somehow I never did get to understand WHY vibration shifts even the highest torgued nut. Must have slept through that lecture. Never found it on the net either.

I'm sure somebody out there can explain it in non mathematical terms.

[skytrek]

Vibration is only a small part of the problem.
During the operating life of an engine it will under go temperature changes
Ranging from freezing to 200f or more.
Metal expands when heated and contracts when cooled.
Different metals expand at different rates when exposed to the same temperature
Engines are made up of different metals ranging from high tinsel steel to diecast alloys. When a high tensile bolt is screwed into an alloy even the tightest bolt can become loose when The engine reaches operating temp too quickly or cooled too quickly (thermal shock)
The wire through the bolt will ensure the bolt will not turn during heat expansion.

[lnuss]

And along that line, temperature changes on aircraft are rather more frequent and rapid than on ground machines. When you lose 3.5º F per thousand feet, and go up 3,000 to 20,000 feet, then back down again an hour or three later...

[P3_Super_Bee]

Also use what we call "Jesus Clips" on turnbarrels, little clips that work like safety wire, lot easier than safety wiring turnbarrels. The name comes from if you don't have 'em "Oh Jesus, I have to safety wire" LOL.

There are also Cotter Keys/Pins Here you have a hole in the bolt, use a castle nut, line up the space in the nut to the hole, slide the pin/key through, split it open wrapping the pin/key around each side of the nut.


http://hometown.aol.com/p3superb/ima...gn_name_lg.jpg

[beetlebailey]

It also prevents forgetfulness. Yes, mechanics do from time to time forget to tighten some bolts. The wire can be a reminder, "hey, I forgot to tighten this bolt."

Beetle

[P3_Super_Bee]

>It also prevents forgetfulness. Yes, mechanics do from time
>to time forget to tighten some bolts. The wire can be a
>reminder, "hey, I forgot to tighten this bolt."
>
>Beetle

This makes no sense what so ever... I'm thinking if you frogot to tighten the bolt, you sure as h311 aren't going to remember to safety wire it...


http://hometown.aol.com/p3superb/ima...gn_name_lg.jpg